Projection device having a mode selection unit

ABSTRACT

The invention relates to a projection device for projecting an image comprising a light source ( 1 ), electro-optical light modulation ( 22 ) and image projection means ( 12 ) for projecting the image. In order to provide a projection device that can be used and is optimized for different modes, such as for video applications and business applications, the projection device according to the present invention further comprises a switchable module ( 3 ) comprising at least a first submodule ( 31 ), and a mode selection unit ( 20 ) for controlling said module ( 3 ) such that said first submodule ( 31 ) is either active or not active in the light path from said light source ( 1 ) to said image projection means ( 12 ), said first submodule ( 31 ) being adapted to improve the center brightness and white point of the light.

The invention relates to a projection device for projecting an imagecomprising a light source, electro-optical light modulation means andimage projection means for projecting the image. The invention alsorelates to a corresponding method of projecting an image.

Projection devices, in particular LCD projection devices, are becomingmore and more popular for business presentations, particularly forpresenting graphic and/or PC data. However, due to the high price, themarket of these projection devices for home video applications is stillmoderate. JP 07 084 553 A therefore proposes a projection liquid crystaldisplay device which is capable of obtaining excellent contrast orluminance in accordance with each picture display and of obtaining anexcellent display picture quality, even in the case of displaying avideo or a PC picture. In this device, the diameter of an aperture whichis located in the imaging path in front of a projection lens iscontrolled by a mode selection circuit. When displaying video data, thediameter of the aperture is reduced, which improves the contrast,whereas the brightness is enhanced when displaying a PC picture in whichthe diameter of the aperture is enlarged.

It is an object of the present invention to provide an alternativesolution for a projection device which can be used and is optimised forat least two different modes and which avoids the need of controlling anaperture in the imaging path.

According to the present invention, this object is achieved by aprojection device as defined in claim 1 which, in addition to the lightsource, the electro-optical light modulation means and the imageprojection means, further comprises a switchable module comprising atleast a first submodule, and a mode selection unit for controlling saidmodule such that said first submodule is either active or not active inthe light path from said light source to said image projection means,said first submodule being adapted to improve the centre brightness andwhite point of the light.

In contrast to the known solution, the switchable module is not locatedin the imaging path within the image projection means or between theimage projection means and a screen, but is located in the light path sothat the light will already be influenced and optimised before itreaches the image projection means. In this way, a much betteroptimisation depending on the type of data (Video, PC) to be convertedinto an image for projection can be achieved. The first submoduleprovided according to the present invention is optimised for videoapplications which require a proper white point to obtain true colours,e.g. correct skin tones. Furthermore, the perceived picture quality forvideo applications is improved when there is more light in the centre ofthe screen with respect to the corners. If, instead of video data,graphic or PC data must be projected, the first submodule can simply bemade inactive by the mode selection unit, e.g. by moving the firstsubmodule out of the light beam. The present invention thus provides aninexpensive, yet very effective solution of a projection device which isusable and optimised for different kinds of applications.

As for contrast, a light distribution across the image provided by thesolution known from JP 07084553 A is not optimised for these twodifferent applications. In the projection device known from thisdocument, only the contrast of the projected image can be improved bypreventing light rays, which traverse the LCD panels at angles where thecontrast is weak, from hitting the screen. This is achieved by reducingthe size of a diaphragm, but this causes a loss of light, leading to alower brightness.

In contrast, the present solution does not focus on contrastoptimisation, but on light distribution across the image. In the case ofdata projection, a very homogeneous light distribution is required, i.e.the corner brightness needs to be almost similar to the centrebrightness. For these images, the white colour is of lesser importance.The best picture performance is thus provided with this kind ofapplication, i.e. a homogeneous illumination with a good colourbrightness and minimum loss of light for colour generation.

In the case of video projection, a different light distribution ispreferred. For these applications, the human eye likes the pictures morewhen the centre brightness is peaked. According to the presentinvention, this is achieved by another integrator module thatdistributes the light across the image in another manner. Compared tothe data mode, light is now taken away from the corner and brought tothe centre. For video, the human eye is very sensitive to proper colours(especially skin colours). This is achieved in this mode with an extrafilter element that balances the colour channels and thus the whitepoint.

Compared to the solution known from JP 07084553 A, the present solutionhas the advantage that the best brightness is achieved in both cases.Colour balancing has a further advantage. If the colour balancing isachieved by modifying the voltages applied to the LCD panels, thisbalancing will influence the contrast in the image. LCD projectionsystems have a limited contrast due to light-leakage of the panels, andthis light-leakage remains identical when the voltages applied to thepanels are modified for proper colour balancing, e.g. if the greenchannel needs to be dimmed by 40%, this will also involve a 40% lowercontrast in the projected image (maximum brightness becomes 40% less,and dark state remains identical). In the case of the colour filter,both the bright state and the dark state are dimmed and the contrast isnot changed.

Preferred embodiments of the invention are defined in the dependentclaims. According to a first embodiment, the module is located betweenthe light source and the light modulation means.

According to another preferred embodiment, the first submodule comprisesan integrator module or a lens unit, particularly comprising two lensesfor improving centre brightness and providing a better videoperformance.

It is further preferred that the first submodule comprises colourbalancing filter means for balancing the light spectrum towards therequired colour coordinates, particularly for video applications foradjusting a proper white point.

Instead of simply making the first submodule inactive when no videoapplication is required, the module further comprises a second submoduleaccording to another preferred embodiment of the invention, which secondsubmodule is adapted to improve corner brightness and intensity of thelight output. The mode selection unit is then adapted to control themodule in such a way that either the first or the second submodule isactive in the light path. The second submodule is thus optimised forbusiness applications, i.e. for projection of graphic or PC data. Thisapplication requires a very homogeneous brightness of the entire image(high corner brightness) and a maximum light output, while a propercolour balancing is not required.

It is advantageous that the mode selection unit is adapted toautomatically control the module based on the type of data to beconverted into an image for projection. In this way, the module switchesautomatically in the correct mode, depending on the type of input data.It is thus preferred that the first submodule is active for video data,whereas the second submodule is active for graphic and/or PC databecause the submodules are optimised for the corresponding applications.

Alternatively or in addition, a user interface can be provided forcontrolling the mode selection unit by a user who will then be able toselect the correct mode.

The invention can be generally applied in any kind of projection device.A preferred application is in LCD projection devices where theelectro-optical light modulation means comprise a three-panel liquidcrystal display as particularly described in WO 01/19092.

The invention will now be explained in more detail with reference to thedrawings, in which

FIG. 1 shows a first embodiment of a projection device according to theinvention, and

FIG. 2 shows a second embodiment of a projection device according to thepresent invention.

The projection device according to the invention shown in FIG. 1comprises a light source 1, i.e. a projection lamp, such as anultra-high pressure (UHP) lamp, having a curved reflector,electro-optical light modulation means 22 and a projection lens 12. Theelectro-optical light modulation means 22 comprise three electro-opticallight modulation panels 4, 5, 6 with which a green (G), a red (R) and ablue (B) part, respectively, of an image to be projected are realized.Furthermore, lenses 9 and (dichroic) folding mirrors 10 are provided insaid light modulation means 22 which are known per se and will thereforenot be described in greater detail. Moreover, the light modulation meanscomprise a dichroic prism 23 arranged between the light modulationpanels 4, 5, 6 and the projection lens 12. For more details of such aprojection device, reference is made to WO 01/19092.

For driving the light modulation means 22, a projection drive unit 19for supplying it with the information about the images to be projectedis provided. The data D, such as video, graphic or PC data, aretherefore applied to the projection drive unit 19.

According to the present invention, a switchable module 3 comprising afirst submodule 31 and a second submodule 32 is provided in the lightpath between the light source 1 and the light modulation means M.Depending on the type of application, either one of said submodules 31,32 is active in the light path while the other one is inactive. Saidactivity is controlled by a mode selection unit 20 which is connected tothe projection drive unit 19 from which it receives information aboutthe kind of data D and/or the kind of application so that the correctsubmodule 31 or 32 can be activated. In addition or alternatively, auser interface 21 can be provided to allow a user to switch between thefirst or the second submodule 31 or 32 via the mode selection unit 20.

The first submodule 31 comprises two (in general, one or more) lenses 34and a spectral filter 33 for white balancing. It is optimised for videoapplications which generally require a proper white point to obtain truecolours. Since the projection lamp 21 is usually deficient in blue andred light, the white point of the light emitted by the projection lampis visibly shifted to green. To correct this in the case of videoapplications, the first submodule comprises the filter element 33 thatbalances the light spectrum towards the proper colour coordinates andadjusts the correct white point. Furthermore, it comprises the lenses 34for improving the perceived picture quality by focussing more light onthe centre of the display with respect to the corners, i.e. the cornerbrightness is reduced as compared with other applications.

The second submodule 32 comprises two lens plates 35 each carrying anumber of lens elements. It is optimised for business applications, suchas the projection of graphic or PC data. In such applications, a highcorner brightness and a maximum light output are required. To maximizethe brightness, no light is “wasted” for proper colour balancing.

Further elements like additional lenses, integrators and/or a polarizingbeam splitter may also be provided but are not shown.

Either one of said submodules 31, 32 can be activated by the modeselection unit 20, e.g. by moving one of said submodules into the lightpath and moving the other submodule out of the light path.

In the embodiment shown in FIG. 2, the submodule 31 does not comprisethe two lenses 34 but video integrator modules 36 comprising a lensplate carrying several lenses.

It should be noted that, according to alternative embodiments of theinvention, the module 3 may only comprise the first submodule 31 whichis activated for video applications, while for other applications thefirst submodule 31 is simply moved out of the light beam so that thelight beam is not influenced at this point. According to still anotherembodiment, the module 3 may also be located at another position withinthe projection device. The invention may generally also be applied inother projection devices, particularly comprising different lightmodulation means.

1. A projection device for projecting an image, comprising: a lightsource, electro-optical light modulation means, image projection meansfor projecting the image, a switchable module comprising at least afirst submodule, and a mode selection unit for controlling said modulesuch that said first submodule is either active or not active in thelight path from said light source to said image projection means, saidfirst submodule being adapted to improve the centre brightness and whitepoint of the light.
 2. A projection device as claimed in claim 1,wherein said module is located between said light source and said lightmodulation means.
 3. A projection device as claimed in claim 1, whereinsaid first submodule comprises an integrator module or a lens unit,particularly comprising two lenses.
 4. A projection device as claimed inclaim 1, wherein said first submodule comprises colour balancing filtermeans for balancing the light spectrum towards the required colourcoordinates.
 5. A projection device as claimed in claim 1, wherein saidmodule further comprises a second submodule adapted to improve cornerbrightness and intensity of the light output, and wherein said modeselection unit is adapted to control said module in such a way thateither said first or said second submodule is active in the light path.6. A projection device as claimed in claim 1, wherein said modeselection unit is adapted to automatically control said module based onthe type of data to be converted into an image for projection.
 7. Aprojection device as claimed in claim 6, wherein said mode selectionunit is adapted in such a way that said first submodule is active forvideo data and that said second submodule is active for graphic and/orPC data.
 8. A projection device as claimed in claim 1, furthercomprising a user interface for controlling said mode selection unit bya user.
 9. A projection device as claimed in claim 1, wherein saidelectro-optical light modulation means comprise a three-panel liquidcrystal display.
 10. A method of projecting an image, comprising thesteps of: generating light by means of a light source, improving thecentre brightness and white point of the light by means of a firstsubmodule, controlling the activity of said first submodule in the lightpath by means of a mode selection unit, modulating the light by means ofan electro-optical light modulation means, projecting the image by meansof an image projection means.